The invention relates to a surgical, tubular-shafted instrument with a shaft, at the distal end of which at least one tool is arranged on a holder which, for its part, is secured in position on the shaft, and with a plastic sheath partially covering the holder.
A tubular-shafted instrument of this type is known, for example, from DE 93 18 815 U1. It is possible with such a tubular-shafted instrument, on the one hand, to use very solid metallic materials for the construction of the holder and the shaft and, on the other hand, to electrically insulate the shaft, including the holder, towards the outside as far as the area of the tools, on the one hand by surrounding the shaft itself with an electrically insulating sleeve, on the other hand by the holder having in certain areas a plastic sheath which covers outwardly pointing areas of the metallic holder. If such a tubular-shafted instrument is used as an electrical cutting and coagulation instrument, it is ensured in this way that any voltage applied to the instrument comes into contact with the body tissue only in the area of the actual tool so that cutting or coagulating occurs only in this area.
In practice, it has been shown that plastic sheaths of this type lift away from the holder in their edge area during the course of time and in this area cavities are formed which can become soiled and are very difficult to clean. This is due, on the one hand, to the fact that the material of the plastic sheath, which is normally applied by way of spraying on, does not combine with the material of the holder; this material may, for example, be high-quality steel. On the other hand, during the sterilization of these tubular-shafted instruments steam possibly penetrates the gap between the plastic sheath and the holder under increased pressure and increases the size of this gap so that the plastic material of the plastic sheath is removed from its areal contact on the holder.
The object of the invention is to design a generic tubular-shafted instrument such that such a lifting of the plastic sheath away from the holder and, in particular, the formation of larger cavities which are difficult to clean are avoided.
This object is accomplished in accordance with the invention, in a surgical tubular-shafted instrument of the type described at the outset, in that the plastic sheath engages at its edge beneath projections on the holder. The connection between the plastic sheath, on the one hand, and the holder, on the other hand, is thus designed such that the holder engages over the adjacent plastic sheath in the edge region and thereby prevents any lifting away from the supporting surface of the holder; in this way, a positive securing in position of the plastic sheath is, in practice, obtained in the edge region.
In a preferred embodiment it is provided for the projections to be formed by undercuts of a step in the holder which limits a lower-lying area of the holder covered by the plastic sheath. Such a step may, for example, extend over the entire circumference of the holder and results in the plastic sheath being secured in position on the holder in the same way along its entire edge.
In this respect, it is advantageous when the backwardly tapering cavity of the undercut is completely filled by the material of the plastic sheath. This results in a complete positive connection and prevents cavities, which can become soiled, being formed at any point.
It is particularly advantageous when the undercut is formed by a boundary surface of the step extending at an angle to the height of the step.
In accordance with a preferred embodiment, it is provided for the plastic sheath to adjoin non-sheathed, adjacent areas of the holder in a stepless manner so that a continuous outer surface is obtained which extends uniformly over the gap between holder surface and plastic sheath surface.
The material of the plastic sheath will preferably be a plastic material which can be sterilized by steam, for example, polyether ether ketone (PEEK) or liquid crystal polymer (LCP).
The following description of preferred embodiments of the invention serves to explain the invention in greater detail in conjunction with the drawings.